Gas turbine outer case active ambient cooling including air exhaust into a sub-ambient region of exhaust flow

ABSTRACT

A gas turbine engine including an outer case extending circumferentially around the central longitudinal axis. A cooling channel is associated with the outer surface of the outer case, the cooling channel having a channel inlet and a channel outlet. An air duct is provided including an inlet end in fluid communication with the channel outlet and an outlet end in fluid communication with an exhaust gas flow from a turbine section of the gas turbine engine. An exit structure is located at the air duct outlet end, and the exit structure provides a sub-ambient pressure at the air duct outlet end to induce a flow from the air duct inlet end to the air duct outlet end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 13/314,311, filed Dec. 8, 2011, which application is herein incorporated by reference in its entirety as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to gas turbine engines and, more particularly, to structures for providing thermal protection to limit heating of the outer case of a gas turbine engine.

BACKGROUND OF THE INVENTION

A gas turbine engine generally includes a compressor section, a combustor section, a turbine section and an exhaust section. In operation, the compressor section may induct ambient air and compress it. The compressed air from the compressor section enters one or more combustors in the combustor section. The compressed air is mixed with the fuel in the combustors, and the air-fuel mixture can be burned in the combustors to form a hot working gas. The hot working gas is routed to the turbine section where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanded gas exiting the turbine section may then be exhausted from the engine via the exhaust section.

In a typical gas turbine engine, bleed air comprising a portion of the compressed air obtained from one or more stages of the compressor may be used as cooling air for cooling components of the turbine section. Additional bleed air may also be supplied to portions of the exhaust section, such as to cool portions of the exhaust section and maintain a turbine exhaust case below a predetermined temperature through a forced convection air flow provided within an outer casing of the engine. Advancements in gas turbine engine technology have resulted in increasing temperatures, and associated outer case deformation due to thermal expansion. Case deformation may increase stresses in the case and in components supported on the case within the engine, such as bearing support struts. The additional stress, which may operate in combination with low cycle fatigue, may contribute to cracks, fractures or failures of the bearing support struts that are mounted to the casing for supporting an exhaust end bearing housing.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a gas turbine engine is provided comprising an outer case defining a central longitudinal axis, and an outer surface of the outer case extending circumferentially around the central longitudinal axis. A cooling channel is associated with the outer surface of the outer case, the cooling channel having a channel inlet and a channel outlet. An air duct is provided including an inlet end in fluid communication with the channel outlet and an outlet end in fluid communication with an exhaust gas flow from a turbine section of said gas turbine engine. An exit structure is located at the air duct outlet end, and the exit structure provides a sub-ambient pressure at the air duct outlet end to induce a flow from the air duct inlet end to the air duct outlet end.

The exit structure may interact with a portion of the exhaust gas flow passing over the exit structure for effecting a reduced pressure at the outlet end to draw air from the cooling channel into the air duct.

The exit structure may partially cover the air duct outlet end, shielding an upstream side of the outlet end and defining a downstream facing opening adjacent a downstream side of the outlet end.

The exit structure may produce a jet pump effect at the air duct outlet end to produce a sub-ambient pressure within the air duct and draw heated cooling air from the cooling channel into the air duct.

The outer case surface may comprise an exterior surface of the outer case, and the cooling channel may be defined by a panel structure located radially outward from the exterior surface.

The cooling channel may extend around the circumference of the outer case.

The channel inlet may be at a first circumferential location, and the channel outlet may be at a second circumferential location circumferentially spaced from the first circumferential location.

The first circumferential location of the channel inlet may be diametrically opposite from the second circumferential location of the channel outlet.

The cooling channel may be located at an axial location of an exhaust diffuser, and the air duct outlet may be located downstream from the exhaust diffuser at an exhaust manifold.

The air duct inlet end may be open to ambient air outside of the gas turbine engine to provide ambient cooling air to the cooling channel.

In accordance with another aspect of the invention, a gas turbine engine is provided comprising an outer case defining a central longitudinal axis, and an outer surface of the outer case extending circumferentially around the central longitudinal axis. An exhaust gas passage is defined within the outer case for conducting an exhaust gas flow from a turbine section of the gas turbine engine. A cooling channel extends circumferentially around the outer surface of outer case, the cooling channel having a channel inlet and a channel outlet located in circumferentially spaced relation to the channel inlet. An air duct is provided including an inlet end in fluid communication with the channel outlet and an outlet end in fluid communication with the exhaust gas flow. An exit structure is located at the air duct outlet end and interacts with the exhaust gas flow for effecting a reduced pressure at the outlet end of the air duct to draw air from the cooling channel into the air duct.

The cooling channel may be located at an axial location of an exhaust diffuser, and the air duct outlet may be located downstream from the exhaust diffuser at an exhaust manifold.

The air duct may be located outside of the outer surface of the outer case and may extend axially between the exhaust diffuser and the exhaust manifold.

The exhaust manifold may include a manifold wall having a manifold outer surface and a manifold inner surface, a manifold opening extending between the manifold outer and inner surfaces, the air duct may be attached to the manifold outer surface and the exit structure may be mounted to the manifold inner surface.

The exit structure may be defined by a plate-like exit shield plate having a first circumferential edge attached to the manifold inner surface upstream of the manifold opening, and the exit shield having a second circumferential edge downstream of the first circumferential edge and spaced radially inwardly from the manifold inner surface.

The air duct may define a central axis extending generally parallel to flow of air through the air duct and the central axis intersects the exit shield.

The exit shield diverts flow of exhaust gas in the exhaust manifold away from the manifold opening and effects the reduced pressure at the outlet end of the air duct.

The gas engine further may include a thermal barrier/cooling system for controlling a temperature of the outer case, the thermal barrier/cooling system including:

-   -   an internal insulating layer supported on an inner surface of         the outer case opposite the outer surface of the outer case, the         internal insulating layer extending circumferentially along the         inner surface of the outer case and providing a thermal         resistance to radiated energy from the exhaust gas passage         located radially inwardly from the outer case; and     -   the cooling channel defined by a panel structure located in         radially spaced relation to the outer surface of the outer case         and extending around the circumference of the outer surface of         the outer case, the cooling channel being generally axially         aligned with the internal insulating layer and forming a flow         path for an ambient air flow cooling the outer surface of the         outer case.

The thermal barrier/cooling system may include an external insulating layer supported on and covering the panel structure.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

FIG. 1 is a cross-sectional elevational view through a portion of a gas turbine engine including an exhaust section illustrating aspects of the present invention;

FIG. 2 is a partially cut-away perspective view of the exhaust section illustrating aspects of the present invention;

FIG. 2A is a perspective view of a lower portion of the structure illustrated in FIG. 2 illustrating a main air inlet;

FIG. 2B is a perspective view from a lower side of the structure illustrated in FIG. 2 illustrating auxiliary air inlets;

FIG. 3 is a cross-sectional axial view of the exhaust section diagrammatically illustrating air flow provided around an outer case of the gas turbine engine;

FIG. 4 is a cut-away perspective view of a portion of the exhaust section adjacent to a top-dead-center location of the exhaust section;

FIG. 5 is a perspective view illustrating an insulating layer segment in accordance with an aspect of the invention;

FIG. 6 is a cross-sectional elevational view through a portion of a gas turbine engine including an exhaust section having an exhaust diffuser and an exhaust manifold illustrating an additional aspect of the present invention including an air duct;

FIG. 7 is a partially cut-away perspective view of the exhaust section illustrating aspects of the present invention shown in FIG. 6;

FIG. 8 is an enlarged perspective view of a manifold opening and exit shield in accordance with aspects of the present invention;

FIG. 8A is a view similar to FIG. 8 showing an alternative configuration for the exit shield; and

FIG. 9 is a perspective view of the exhaust section and exhaust manifold illustrating the air duct of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

Referring to FIG. 1, a portion of an exhaust section 10 of a gas turbine engine is shown located axially downstream from a turbine section 12 to illustrate aspects of the present invention. The exhaust section 10 generally comprises a cylindrical structure comprising an outer case 11 extending circumferentially around a generally horizontal central longitudinal axis A_(C) and forms a downstream extension of an outer case the gas turbine engine. The outer case 11 of the exhaust section 10 includes an exhaust cylinder or turbine exhaust case 14, and an exhaust spool structure 16 located downstream from the exhaust case 14.

The exhaust case 14 includes a downstream exhaust case flange 18 that extends radially outwardly of a downstream end the exhaust case 14, and the spool structure 16 includes an upstream spool structure flange 20 that extends radially outwardly of the spool structure 16. The downstream exhaust case flange 18 and upstream spool structure flange 20 abut each other at a joint 22, and may be held together in a conventional manner, such as by bolts (not shown). In addition, an upstream exhaust case flange 21 extends radially outwardly from an upstream end of the exhaust case 14 and may be bolted to a radially extending flange 23 of the turbine section 12 for supporting the exhaust case 14 to the turbine section 12.

The exhaust case 14 comprises a relatively thick wall forming a structural member or frame for supporting an exhaust end bearing housing 24 and for supporting at least a portion of an exhaust diffuser 26. The exhaust end bearing housing 24 is located for supporting an end of a rotor 25 for the gas turbine engine.

The diffuser 26 comprises an inner wall 28 and an outer wall 30 defining an annular passage for conveying hot exhaust gases 31 from the turbine section 12. The bearing housing 24 is supported by a plurality of strut structures 32. Each of the strut structures 32 include a strut 34 extending from a connection 36 on the exhaust case 14, through the diffuser 26, to a connection 38 on the bearing housing 24 for supporting and maintaining the bearing housing 24 at a centered location within the exhaust case 14. The strut structures 32 may additionally include a strut shield or fairing 40 surrounding the strut 34 for isolating the strut 34 from the hot exhaust gases 31 passing through the diffuser 26, see also FIG. 3.

As a result of the hot exhaust gases 31 passing through the diffuser 26, the outer wall 30 of the diffuser 26 radiates heat radially outwardly toward an inner case surface 42 of the exhaust case 14. As discussed above, conventional designs for cooling a turbine exhaust section may provide bleed air supplied from a compressor section of the engine to the exhaust section to provide a flow of cooling air between the diffuser and the exhaust case in order to control or reduce the temperature of the exhaust case through forced convection. In accordance with an aspect of the invention, a thermal barrier/cooling system 44 is provided to reduce and/or eliminate the use of compressor bleed air to control the temperature of the exhaust case 14 and spool structure 16.

Referring to FIGS. 2 and 3, the thermal barrier/cooling system 44 generally comprises an internal insulating layer 46 and a convective cooling channel 48. The internal insulating layer 46 is supported on the inner case surface 42 and extends circumferentially to cover substantially the entire inner case surface 42. The internal insulating layer 46 forms a thermal barrier between the diffuser 26 and the exhaust case 14 to provide a thermal resistance to radiated energy from the outer wall 30 of the diffuser 26.

The internal insulating layer 46 is preferably formed by a plurality of insulating layer segments 46 a (FIG. 5) generally located in side-by-side relation to each other, and having a longitudinal or axial extent that is about equal to the axial length of the exhaust case 14 to provide a thermal barrier across substantially the entire inner case surface 42 of the exhaust case 14. Hence, a substantial portion of the radiated heat from the diffuser 26 is prevented from reaching the exhaust case 14, thereby isolating the wall of the exhaust case 14 from the thermal load contained within the exhaust case 14.

Referring further to FIG. 5, the insulating layer segments 46 a may comprise rectangular segment members having a leading edge 50, a trailing edge 52, and opposing side edges 54, 56. The insulating layer segments 46 a have a lower thermal conductivity than that of the wall of the exhaust case 14. The thermal conductivity of the insulating layer segments 46 a may have a maximum value of about 0.15 W/m·K, and preferably have a thermal conductivity value of about 0.005 W/m·K for resisting transfer of heat from the diffuser to the engine case 14. The insulating layer segments 46 a may positioned on the inner case surface 42 of the exhaust case 14 with the side edges 54, 56 of one insulating layer segment 46 a closely adjacent, or engaged with, the side edges 54, 56 of an adjacent insulating layer segment 46 a.

The construction of the insulating layer segments 46 a may comprise a pair of opposing sheet metal layers 58, 60, and a thermal blanket layer 62 located between the sheet metal layers 58, 60 and having a substantially lower thermal conductivity than the sheet metal layers 58, 60. A plurality of metal bushings 64 may extend through the sheet metal layers 58, 60 and the thermal blanket layer 62 at mounting points for the insulating layer segments 46 a. In particular, each of the metal bushings 64 comprise a rigid structure defining a predetermined spacing between the sheet metal layers 58, 60, and are adapted to receive a fastener structure, such as a standoff 66 (FIG. 4), for attaching each insulating layer segment 46 a to the exhaust case 14. The standoffs 66 may be configured to permit limited movement of the insulating layer segments 46 a relative to the inner case surface 42, such as to provide for any thermal mismatch between the internal insulating layer 46 and the exhaust case 14. For example the standoffs 66 may each comprise a stud 67 having a radially outer end affixed at the inner case surface 42 and having a threaded radially inner end for receiving a nut 69 to retain the insulating layer segment 46 a between the nut and the inner case surface 42.

The insulating layer segments 46 a may be provided with slots 65 extending from the trailing edge 52 to a rear row of the bushings 64 to facilitate assembly of the insulating layer segments 46 a to the exhaust case 14. In particular, the slots 65 facilitate movement of the insulating layer segments 46 a onto the studs 67 during assembly by permitting a degree of axial movement of the rear row of bushings 64 onto a corresponding row of studs 67 at a rear portion of the exhaust case 14 where there is a minimal space between the exhaust case 14 and the diffuser 26.

It may be noted that a limited spacing may be provided between adjacent insulating layer segments 46 a at particular locations around the inner case surface 42. For example, at the locations of the connections 36 where the struts 34 extend inwardly from the inner case surface 42 a spacing or gap may be provided between adjacent insulating layer segments 46 a located adjacent to either side of each strut 34. Similarly, a limited gap may be present between the insulating layer segments 46 a that are directly adjacent to structure forming the horizontal joints 92. It may be noted that an alternative configuration of the insulating layer segments 46 a may be provided to reduce gaps at these locations. For example, the insulating layer segments 46 a may be configured to include portions that extend closely around the struts 34 and thereby reduce gap areas that may expose the inner case surface 42 to radiated heat.

Provision of multiple insulating layer segments 46 a facilitates assembly of the internal insulating layer 46 to the engine case 14, and further enables repair of a select portion of the internal insulating layer 46. For example, in the event of damage to a portion of the internal insulating layer 46, the configuration of the internal insulating layer 46 permits removal and replacement of individual ones of the insulating layer segments 46 a that may have damage, without requiring replacement of the entire internal insulating layer 46.

It should be understood that although a particular construction of the insulating layer segments 46 a has been described, other materials and constructions for the insulating layer segments 46 a may be provided. For example, the insulating layer segments 46 a may be formed of a known ceramic insulating material configured to provide a thermal resistance for surfaces, such as the inner case surface 42.

Referring to FIG. 1, the convective cooling channel 48 extends circumferentially around an outer case surface 68 of the exhaust case 14, and is generally axially located extending from the upstream exhaust case flange 21 to at least the downstream exhaust case flange 18, and preferably extending to a downstream spool structure flange 70 extending radially outwardly from a downstream end of the spool structure 16. The convective cooling channel 48 is defined by a panel structure 72 that extends from an upstream location 74 where it is affixed to the exhaust section 10 at the upstream exhaust case flange 21 to a downstream location 76 where it is affixed to the exhaust section 10 at the downstream spool structure flange 70. The panel structure 72 is located in radially spaced relation to the outer case surface 68 to define a first cooling channel portion 78 of the convective cooling channel 48, i.e., a recessed area between the upstream exhaust case flange 21 and the downstream exhaust case flange 18. The panel structure 72 is further located in radially spaced relation to an outer surface 80 of the spool structure 16 to define a second cooling channel portion 82 of the convective cooling channel 48, i.e., a recessed area between the upstream spool structure flange 20 and the downstream spool structure flange 70. The first and second cooling channel portions 78, 82 define circumferentially parallel flow paths around the exhaust section 10 and may be in fluid communication with each other across the radially outer ends of the flanges 18, 20.

Referring to FIGS. 2 and 3, the convective cooling channel 48 includes a main cooling air supply inlet 84 located at a first circumferential location for providing a supply of ambient air to the convective cooling channel 48. The convective cooling channel 48 further includes an exhaust air outlet 86 at a second circumferential location that is diametrically opposite from the first circumferential location. In accordance with a preferred embodiment, the main air supply inlet 84 (FIG. 2A) is located at a bottom-dead-center location of the outer case 11 of the exhaust section 10, and the exhaust air outlet 86 is located at a top-dead-center location of the outer case 11 of the exhaust section 10.

As seen in FIG. 2, the exhaust section 10 may be formed in two halves, i.e., an upper half 88 and a lower half 90, joined together at a horizontal joint 92. In accordance with an aspect of the invention, the panel structure 72 includes enlarged side portions 94 formed as box sections extending across the horizontal joints 92 from locations above and below the horizontal joints 92. The side portions 94 are configured to provide additional clearance for air flow around the horizontal joints 92, and may further be configured to provide an additional air flow to the convective cooling channel 48, as is discussed below.

The panel structure 72 comprises individual panel sections 72 a that may be formed of sheet metal, i.e., relatively thin compared to the outer case 11. The panel sections 72 a are curved to match the curvature of the outer case 11, and extend downwardly from the side portions 94 toward the main air inlet 84, and extend upwardly from the side portions 94 toward the air outlet 86. The panel sections 72 a are formed as generally rectangular sections extending between the upstream and downstream locations 74, 76 on the exhaust section 10, and preferably engage or abut each other, as well as the side portions 94 at shiplap joints 98 along axially extending edges of the panel sections 72 a. The panel sections 72 a and side portions 94 may be attached to the exhaust section outer case 11 by any conventional means, and are preferably attached as removable components by fasteners, such as bolts or screws. It should be understood that although the enlarged side portions 94 are depicted as box sections, this portion of the panel structure 72 need not be limited to a particular shape and may be any configuration to facilitate passage of air flow past the horizontal joints 92, which typically comprise enlarged and radially outwardly extending flange portions of the exhaust section outer case 11. Further, it should be noted that the main air inlet 84 and the air outlet 86 may incorporated into respective panel sections 72 a at respective bottom-dead-center and top-dead-center locations around the panel structure 72.

Referring to FIGS. 2 and 2B, the side portions 94 may be formed with a lower portion 100 extending below the horizontal joints 92 and terminating at a downward facing auxiliary air inlet structure 102. The auxiliary air inlet structure 102 may include first and second auxiliary air inlet openings 104, 106 located side-by-side, each of which is illustrated as a downwardly facing opening in the panel structure 72. The first and second auxiliary air inlet openings 104, 106 may be axially aligned over the first and second channel portions 78, 82, respectively. The auxiliary air inlet openings 104, 106 are shown as being provided with respective cover panels or plates 108, 110 that may be removably attached over the openings with fasteners 112, such as bolts or screws. One or both of the cover plates 108, 110 may be displaced or removed from the auxiliary air inlet openings 104, 106 to permit additional or auxiliary ambient air 116 into the convective cooling channel 48 through the auxiliary air inlet structure 102, as is further illustrated in FIG. 3.

In accordance with an aspect of the invention, the convective cooling channel 48 receives a non-forced ambient air through the main air supply inlet 84. That is, air may be provided to the convective cooling channel 48 without a driving or pressure force at the air inlet 84 to convey air in a convective main air supply flow 114 from a location outside the gas turbine engine through the main air supply inlet 84. The main air supply inlet 84 may be sized with a diameter to extend across at least a portion of each of the first and second channel portions 78, 82, such that a portion of the main supply air flow 114 may pass directly into each of the channel portions 78, 82.

The ambient air flow into the convective cooling channel 48 provides a decreased thermal gradient around the circumference of the exhaust section 10 to reduce or minimize thermal stresses that may occur with a non-uniform temperature distribution about the exhaust section 10. In particular, stresses related to differential thermal expansion of the exhaust case 14, and transmitted to the struts 34, may be decreased by the increased uniformity of the cooling flow provided by the convective cooling channel 48. Further, the operating temperature of the exhaust case 14 may be maintained below the material creep limit to avoid associated case creep deformation that may cause an increase in strut stresses.

A multiport cooling configuration may be provided for the convective cooling channel 48 by displacing or removing one or more of the cover plates 108, 110 of the auxiliary air inlet structure 102 to increase the number of convective cooling air supply locations. Hence, the amount of cooling provided to the channel portions 78, 82 may be adjusted on turbine engines located in the field to increase or decrease cooling by removal or replacement of the cover plates 108, 110. For example, it may be desirable to provide an increase in the cooling air flow by removing one or more of the cover plates 108, 110, or it may be desirable to provide a decrease in air flow by replacing one or more of the cover plates 108, 110 to prevent or decrease the auxiliary air flow 116, depending on increases or decreases in the ambient air temperature. Further, the cover plates 108, 110 may be used optimize the temperature of the exhaust case 14 and spool structure 16 to minimize any thermal mismatch between adjacent hardware and components.

The exhaust air outlet 86 is located at the top of the convective cooling channel 48, such that the heated exhaust air 118 may flow by convection out of the convective cooling channel 48. The exhaust air outlet 86 may be sized with a diameter to extend across at least a portion of each of the first and second channel portions 78, 82, such that the heated air exhausting from the convective cooling channel 48 may be conveyed directly to the exhaust air outlet 86 from each of the channel portions 78, 82. Subsequently, the heated air passing out of the exhaust air outlet 86 may be exhausted out of existing louver structure (not shown) currently provided for existing gas turbine engine units.

It should be understood that the convective air flow through the convective cooling channel 48 comprises a cooling air flow that may be substantially driven by a convective force produced by air heated along the outer case surface 68 and outer surface 80 of the spool structure 16. The heated air within the convective cooling channel 48 rises by natural convection and is guided toward the exhaust air outlet 86. As the air rises within the convective cooling channel 48, it draws ambient air into the channel 48 through the main cooling air supply inlet 84, effectively providing a driving force for a continuous flow of cooling air upwardly around the outer surface of the outer case 11. Similarly, when either or both of the auxiliary air inlet openings 104, 106 on the sides of the panel structure 72 are opened, natural convection will draw the air upwardly around the channel 48 through the auxiliary air inlet structure 102 to the exhaust air outlet 86.

It may be noted that as the cooling air flows upwardly as a convection air flow 48, a lower pressure will be created within the convective cooling channel 48 than the ambient air pressure outside the convective cooling channel 48. Hence, any leakage at the panel joints 98, or the joints 97, 99 (FIG. 2) where the edges of the panel segments 72 a are mounted to the exhaust section 10 at the upstream and downstream locations 74, 76, will occur inwardly into the convection cooling channel 48. In this regard, it may be understood that it is not necessary to provide a leakage-proof sealing at the peripheral edges of the panel segments 72 a and side portions 94, and that leakage into the convective cooling channel 48 may be viewed as an advantage facilitating the cooling function of the thermal barrier/cooling system 44.

Optionally, as is illustrated diagrammatically in FIG. 3, a fan unit 120 may be provided connected to the exhaust air outlet 86. The fan unit 120 may provide additional air flow from the exhaust air outlet 86 to increase the cooling capacity of the convective cooling channel 48, while maintaining an ambient airflow into and through the convective cooling channel 48. Alternatively, or in addition, an inlet fan unit (not shown) may be provided to the main cooling air supply inlet 84 to provide an increase in the ambient airflow into the channel 48. It should be understood that even with the provision of a fan unit to facilitate flow through the convective cooling channel 48, i.e., a fan unit 120 at the outlet 86 and/or a fan unit at the inlet 84, the movement of the air flow through the channel 48 may create a reduced pressure within the channel 48 relative to the ambient area surrounding the outside of the outer case 11.

The convective cooling channel 48 may further be provided with an external insulating layer 122, as seen in FIGS. 1, 3, and 4 (not shown in FIG. 2). The external insulating layer may cover substantially the entire exterior surface of the panel structure 72 defined by the panel segments 72 a and side portions 94, and has a low thermal conductivity to generally provide thermal protection to personnel working or passing near the exhaust section 10.

Referring to FIG. 4, an optional further or second internal insulating layer 124 may be provided to the spool structure 16, extending circumferentially around an inner spool segment surface 126, radially outwardly from a Z-plate or spring plate structure 128 provided for supporting the diffuser 26. The second internal insulating layer 124 may comprise separate insulating layer segments having a construction and thermal conductivity similar to that described for the internal insulating layer 46. Further, the second internal insulating layer 124 may be mounted to the inner spool segment surface 126 in a manner similar to that described for the insulating layer segments 46 a of the internal insulating layer 46. The second internal insulating layer 124 may be provided to limit or minimize an amount of radiated heat transmitted from the diffuser 26 to the spool structure 16. Hence, the convective air flow requirement for air flowing through the second portion 82 of the convective cooling channel 48 may be reduced by including the second internal insulating layer 124.

As described above, the thermal barrier/cooling system 44 provides a system wherein the internal insulating layer 46 substantially reduces the amount of thermal energy transferred to the outer case 11 of the exhaust section 10, and thereby reduces the cooling requirement for maintaining the material of the outer case 11 below its creep limit. Hence, the external cooling configuration provided by the convective cooling channel 48 provides adequate cooling to the outer case 11 with a convective air flow, with an accompanying reduction or elimination of the need for forced air cooling provided to the interior of the outer case 11. Elimination of forced air cooling to the interior of the outer case 11, i.e., by maintaining supply and exhaust of cooling air external to the outer case 11, avoids problems associated with thermal mismatch or thermal gradients between components within the outer case 11.

Additionally, since the air supply for cooling the outer case 11 does not draw on compressor bleed air or otherwise directly depend on a supply of the air from the gas turbine engine, the present thermal barrier/cooling system 44 does not reduce turbine power, such as may occur with systems drawing compressor bleed air, and the cooling effectiveness of the present system operates substantially independently of the engine operating conditions. Hence, the present invention may be implemented without drawing on the secondary cooling air of the gas turbine engine, and may provide a reduced requirement for usage of secondary cooling air with an associated increase in overall efficiency in the operation of the gas turbine engine.

In accordance with an alternative aspect of the invention, the flow through the cooling channel 48 may be actively formed by using a source of sub-ambient pressure within the engine 10. In accordance with this aspect, and referring to FIGS. 6-9, a source of sub-ambient pressure may be attached to the exhaust air outlet 86 illustrated in FIGS. 2, 3 and 4. In particular, as is shown in FIGS. 6, 7 and 9, an air duct 130 is attached to the exhaust air outlet 86 of the cooling channel 48 for providing a sub-ambient pressure to the air outlet 86 in order to actively effect a flow of ambient air though the cooling channel 48.

The air duct 130 includes a conduit, such as a conduit defining a generally circular or similar cross-section, having an inlet end 132 attached to the air outlet 86 and extending to an outlet end 134 which is in fluid communication with exhaust gases 31 passing through an exhaust manifold 136. As illustrated herein, the air duct 130 includes a first section 130 a extending radially, a second section 130 b extending axially, and a third section 130 c extending radially and generally parallel to the first section 130 a. The first section 130 a may be formed with an enlarged portion at the inlet end 132 to correspond to the size and shape of the air outlet 86. Further, in order to accommodate thermal deflection that may result in relative movement in the radial and axial directions between the air duct 130 and the exhaust section outer case 11 and exhaust manifold 136, the air duct 130 may be provided with bellows structures 131, as is illustrated by the bellows structures 131 on the second and third sections 130 b and 130 c.

The exhaust manifold 136 is attached to a downstream end of the outer case 11 for receiving exhaust gas passing to the exit of the diffuser 26. The exhaust manifold 136 includes a manifold outer surface 138, a manifold inner surface 140 and a manifold opening 142 extending between the manifold outer and inner surfaces 138, 140.

The outlet end 134 of the air duct 130 is bolted or otherwise attached to the manifold outer surface 138 at the manifold opening 142, such that the air duct 130 provides a fluid path placing the cooling channel 48 in fluid communication with the exhaust flow 31 passing through the exhaust manifold 136.

Referring additionally to FIG. 8, an exit structure 144 is attached to the manifold inner surface 140 at the location of the manifold opening 142 and air duct outlet end 134. The exit structure 144 is defined by a plate-like exit shield 146 having a first circumferential edge 148 attached to the manifold inner surface 140 upstream of the manifold opening 142, and a second circumferential edge 150 located axially downstream of the first circumferential edge 148 and spaced radially inwardly from the manifold inner surface 140. Further, opposing side edges 152, 154 extend axially between the first and second circumferential edges 148, 150. The opposing side edges 152, 154 may extend generally parallel to each other in the axial direction. Optionally, a pair of radially extending legs 156, 158 may be located adjacent to the side edges 152, 154 at the downstream second circumferential edge 150, and extend to an attachment point on the manifold inner surface 140 for supporting the second circumferential edge 150 at a predetermined radial spacing from the manifold opening 142. The legs 156, 158 also increase the compliance of the exit shield 146 to enable the exit structure 144 to withstand thermally induced stresses.

The air duct 130 defines a central axis 160 (FIG. 6) extending generally parallel to flow of air through the air duct 130, and the central axis 160 intersects the exit shield 146. Hence, the exit shield 146 is located at the circumferential and axial location of the manifold opening 142. Further, the exit shield 146 preferably has a circumferential dimension, parallel to the edges 148, 150, that is greater than the diameter of the manifold opening 142, such that the exit shield 146 provides a cover that overlaps to either side of the manifold opening 142, extending in the axial direction. The exit shield 146 has an axial extent that begins upstream of the manifold opening 142 and that substantially covers the manifold opening 142 to, or close to, an axially downstream edge 142 a of the manifold opening 142 (FIG. 6). The exit shield 146 diverts flow of exhaust gases in the exhaust manifold 136 radially inward from the manifold inner surface 140 and away from the manifold opening 142, and produces a “jet pump” effect at the downstream edge 150 of the exit shield 146, effecting a reduced (sub-ambient) pressure at the outlet end 134 of the air duct 130.

The reduced or sub-ambient pressure created at the manifold opening 142 induces a flow of air from the air duct 130 into the exhaust manifold 136, and creates a sub-ambient pressure at the exhaust air outlet 86 of the cooling channel 48. The sub-ambient pressure at the exhaust air outlet 86 operates to actively produce a flow of air around the circumference of the outer case 11 through the cooling channel 48, facilitating the upward convective flow in the channel 48 previously described, and drawing ambient cooling air into the channel 48 through the cooling air supply inlet 84 (FIG. 7). Hence, it may be understood that the present aspect of the invention provides a flow connection between a sub-ambient pressure area in the engine, i.e., the exhaust manifold gas passage at the manifold opening 142, and the ambient cooling air supply inlet 84 to actively produce or facilitate a flow of ambient cooling air without drawing on turbine power of the engine.

As noted above, the side edges 152, 154 are provided with the legs 156, 158 to increase the thermal compliance of the exit structure 144. This configuration of the exit structure 144 may also be beneficial in embodiments of the invention where the manifold opening 142 is located at or adjacent to a restricted flow area that limits or restricts the size of the opening between the downstream edge 150 and the manifold opening 144, and where an additional opening area, i.e., along the sides, may be needed to facilitate the “jet pump” effect. Alternatively, side panels 153, 155 (FIG. 8A) may be formed extending from the side edges 152, 154 to the manifold inner wall 140, and shaped to facilitate the “jet pump” effect for increasing the flow of air through the duct 130 and cooling channel 148.

It should be understood that the aspects of the invention utilizing sub-ambient pressure to draw the ambient air through the cooling channel 48 and into the exhaust manifold 136 may be used in combination with any of the aspects of the invention described above, including the aspects of the external insulating layer 122 and internal insulating layers 46, 124 described above. However, it should be noted that the present aspects of the invention, providing the active ambient air flow through the duct 130, may be implemented independently of the aspects described above for providing insulating layers to the outer case 11. For example, although the internal insulating layers 46, 124 are helpful to controlling the temperature of the outer case 11, these layers are not necessary to the operation of the sub-ambient flow through the air duct 130 and the cooling flow provided through the cooling channel 48.

Also, with regard to the panel structure 72 described above for forming the cooling channel 48, the panels 72 a forming the panel structure 72 may be configured to permit ambient air to enter the cooling channel 48 at select locations around the outer case 11. For example, certain locations on the outer case 11 may be subject to localized heating or hot spots, and additional removable panels 72 a or panels 72 a with removable windows or any other opening configuration may be provided to permit an inflow of ambient air through the panel structure 72 substantially directly, or closer, to the hot spots to provide cooler air at these locations than may be provided by the flow of air that has warmed while passing through the cooling channel 48.

A further aspect described above that may be incorporated with present embodiment utilizing the air duct 130 includes providing a blower, such as is described above with reference to the fan unit 120 in FIG. 3, wherein the blower may be provided to a location along the air duct 130, or at the inlet 84 to the cooling channel 48, to create an additional air flow through the duct 130 and facilitate the cooling effect in the cooling channel 48.

Additionally, it may be understood that the cooling channel 48 may be provided to other casings of the engine 10, such as to a turbine casing, a compressor casing, a combustor casing of the engine 10, or any other location that cooling may be required on the engine.

Further, it may be noted that in accordance with aspects of the invention, the duct providing a flow connection to a sub-ambient location formed by exhaust gas flow may extend to any location in the exhaust gas flow, including locations within the turbine exhaust case 14 radially inwardly from the cooling channel 48. For example, structure defining a duct may extend through one or more of the strut structures 32 and have structure defining an axially downstream extending outlet in fluid communication with the gas flow through the diffuser 26 at or adjacent to a trailing edge of the strut structure 32, where the a portion of the strut shield or fairing 40 may provide the sub-ambient effect of the exit structure 144. A passage through the duct structure 32 forming a radially extending air flow connection may be formed, for example, by a radiation shield extending within the duct structure 32 and have a radially outer end in fluid communication with the cooling channel 48 in a manner such as is set out in the concurrently filed Application U.S. Ser. No. ______ (Attorney Docket No. 2011P20816US) entitled GAS TURBINE OUTER CASE ACTIVE AMBIENT COOLING INCLUDING AIR EXHAUST INTO SUB-AMBIENT CAVITY, which is hereby incorporated by reference herein. In this configuration, one or more ducts may form passages from the interior region of the strut structure 32 that is in fluid communication with the cooling channel 48 to an exterior surface of the fairing 40.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

What is claimed is:
 1. A gas turbine engine comprising: an outer case defining a central longitudinal axis, and an outer surface of said outer case extending circumferentially around the central longitudinal axis; a cooling channel associated with said outer surface of said outer case, said cooling channel having a channel inlet and a channel outlet; an air duct including an inlet end in fluid communication with the channel outlet and an outlet end in fluid communication with an exhaust gas flow from a turbine section of said gas turbine engine; and an exit structure at said air duct outlet end, said exit structure providing a sub-ambient pressure at said air duct outlet end to induce a flow from said air duct inlet end to said air duct outlet end.
 2. The gas turbine engine of claim 1, wherein said exit structure interacts with a portion of said exhaust gas flow passing over said exit structure for effecting a reduced pressure at said outlet end to draw air from said cooling channel into said air duct.
 3. The gas turbine engine of claim 2, wherein said exit structure partially covers said air duct outlet end, shielding an upstream side of said outlet end and defining a downstream facing opening adjacent a downstream side of said outlet end.
 4. The gas turbine engine of claim 1, wherein said exit structure produces a jet pump effect at said air duct outlet end to produce a sub-ambient pressure within said air duct and draw heated cooling air from said cooling channel into said air duct.
 5. The gas turbine engine of claim 1, wherein said outer case surface comprises an exterior surface of said outer case, and said cooling channel is defined by a panel structure located radially outward from said exterior surface.
 6. The gas turbine engine of claim 5, wherein said cooling channel extends around the circumference of said outer case.
 7. The gas turbine engine of claim 6, wherein said channel inlet is at a first circumferential location, and said channel outlet is at a second circumferential location circumferentially spaced from said first circumferential location.
 8. The gas turbine engine of claim 7, wherein said first circumferential location of said channel inlet is diametrically opposite from said second circumferential location of said channel outlet.
 9. The gas turbine engine of claim 1, wherein said cooling channel is located at an axial location of an exhaust diffuser, and said air duct outlet is located downstream from said exhaust diffuser at an exhaust manifold.
 10. The gas turbine engine of claim 1, wherein said air duct inlet end is open to ambient air outside of said gas turbine engine to provide ambient cooling air to said cooling channel.
 11. A gas turbine engine comprising: an outer case defining a central longitudinal axis, and an outer surface of said outer case extending circumferentially around the central longitudinal axis; an exhaust gas passage defined within said outer case for conducting an exhaust gas flow from a turbine section of said gas turbine engine; a cooling channel extending circumferentially around said outer surface of outer case, said cooling channel having a channel inlet and a channel outlet located in circumferentially spaced relation to said channel inlet; an air duct including an inlet end in fluid communication with the channel outlet and an outlet end in fluid communication with the exhaust gas flow; and an exit structure at said air duct outlet end interacting with said exhaust gas flow for effecting a reduced pressure at said outlet end of said air duct to draw air from said cooling channel into said air duct.
 12. The gas turbine engine of claim 11, wherein said cooling channel is located at an axial location of an exhaust diffuser, and said air duct outlet is located downstream from said exhaust diffuser at an exhaust manifold.
 13. The gas turbine engine of claim 12, wherein said air duct is located outside of said outer surface of said outer case and extends axially between said exhaust diffuser and said exhaust manifold.
 14. The gas turbine engine of claim 12, wherein said exhaust manifold includes a manifold wall having a manifold outer surface and a manifold inner surface, a manifold opening extending between said manifold outer and inner surfaces, said air duct is attached to said manifold outer surface and said exit structure is mounted to said manifold inner surface.
 15. The gas turbine engine of claim 14, wherein said exit structure is defined by a plate-like exit shield plate having a first circumferential edge attached to the said manifold inner surface upstream of said manifold opening, and said exit shield having a second circumferential edge downstream of said first circumferential edge and spaced radially inwardly from said manifold inner surface.
 16. The gas turbine engine of claim 15, wherein said air duct defines a central axis extending generally parallel to flow of air through said air duct and said central axis intersects said exit shield.
 17. The gas turbine engine of claim 15, wherein said exit shield diverts flow of exhaust gas in said exhaust manifold away from said manifold opening and effects said reduced pressure at said outlet end of said air duct.
 18. The gas turbine engine of claim 11, including a thermal barrier/cooling system for controlling a temperature of the outer case, said thermal barrier/cooling system including: an internal insulating layer supported on an inner surface of said outer case opposite said outer surface of said outer case, the internal insulating layer extending circumferentially along said inner surface of said outer case and providing a thermal resistance to radiated energy from said exhaust gas passage located radially inwardly from said outer case; and said cooling channel defined by a panel structure located in radially spaced relation to said outer surface of said outer case and extending around the circumference of said outer surface of said outer case, said cooling channel being generally axially aligned with said internal insulating layer and forming a flow path for an ambient air flow cooling said outer surface of said outer case.
 19. The gas turbine engine of claim 18, including an external insulating layer supported on and covering said panel structure. 